Since the first release of LTE, automatic neighbour relation (ANR) functionality has been introduced to automatically generate the relations between eNBs. Such relations are used to establish connections between eNBs, support mobility, load balancing, dual connectivity, etc., and hence, ANR may reduce planning and operation costs for operators.
In LTE, a user equipment (UE), also referred to as a wireless device, may detect cells based on their primary/secondary synchronization signals (PSS/SSS), which encode a physical cell identifier (PCI). A property of these signals is that the UE may autonomously detect neighbor cell IDs from an acquired PSS/SSS, i.e., the network does not need to provide a neighbor cell list. UEs may detect and measure neighbor cells by sampling a short time window (e.g., 5 ms) on the target frequency (which may be the same or different from serving) and search (possibly offline) for PSS/SSS occurrences within that sample. For each detected PSS/SSS, the UE can also perform a measurement using the cell reference signal (CRS) corresponding to the PCI. The result of that action is a list of neighbor cell identities and corresponding measurement samples.
Once the UE performs measurements, mobility events can trigger the transmission of measurement reports. Based on these reports, the serving base station eNB is able to identify that a given PCI belongs to a neighbour eNB in order to trigger a handover preparation procedure. In order to do that, the serving eNB may needs to maintain a neighbor relation table (NRT) that maps locally unique identifiers, i.e. the PCIs in LTE, with globally unique identifiers, i.e. the EUTRAN cell global identifier (E-CGI). E-CGI is defined in LTE as a combination of PLMN (Public Land Mobile Network) ID (e.g., a combination of country code and network code) and enhanced cell identity (ECI) (combination of eNB ID and cell ID).
Given the benefits of ANR in LTE, ANR may continue to be an important feature in next generation radio systems, denoted by NR. The challenging NR requirements may be expected to result in an even higher emphasis on seamless mobility than in legacy radio access technologies (RATs), which may further increase the importance of automatic relation establishment in NR. In fact, it has been agreed that ANR will be supported in NR, using LTE procedures as a baseline. Moreover, in RAN WG2 #98-Ad Hoc meeting, it has been agreed that the LTE inter-RAT ANR framework is extended to also cover NR.
A wireless terminal, however, may not be able to receive a CGI of a neighbor cell.